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Study finds flu vaccine benefits for older workers

Jan 14, 2009 (CIDRAP News) – Workers ages 50 to 64 who get their annual flu shots miss less work and experience less of a productivity drop-off than those who don't, according to a new study, findings that might help public officials lift immunization rates among this age-group.

Authors from the Minneapolis Veterans Affairs Medical Center and the University of Minnesota, who published their report in the Feb 1 issue of Clinical Infectious Diseases (CID), wrote that scarce information on the impact of the flu and on the benefits of vaccination in this age-group might be one reason for low vaccination rates in this group.

This, in spite of the fact that workers in this age range have been targeted for influenza vaccines since the 2000-2001 flu season.

Kristin L. Nichol, MD, MPH, lead author of the study, said yesterday in a press release from the Infectious Diseases Society of America (IDSA) that concerns this flu season about antiviral resistance highlight the importance of immunizations. "This study is a reminder of the importance of the influenza vaccine. It's not too late to get your flu shot," she said.

To gauge the impact of the flu shots on workers in the 50- to 64-year-old age-group, Nichol and her colleagues conducted an Internet survey of workers at the University of Minnesota during the 2006-2007 influenza season.

Health and workplace impactsThe research group collected data at baseline in October 2006 and at follow-up intervals from November through April. An influenza-like illness (ILI) was defined as having a fever or feeling feverish with a cough or sore throat.

To identify bias in the study, the researchers compared the risk of non–upper respiratory illnesses during influenza season of the vaccinated participants with those who didn't receive a vaccine. They also calculated the risk of ILI during non-influenza months.

Of the 497 people who were included in the study, 404 (81%) had received an influenza vaccination. Eighty-five (17.1%) of the subjects reported having an ILI during the flu season. Those who reported having ILIs said they were sick an average of 8 days, missed about 1.5 days of work because of their illness, and worked more than 4 days while they were still sick.

The group's self-reported productivity on days they worked while sick was 70% to 75%.

For the unvaccinated group, ILI was responsible for 45% of all illness-days, 39% of all work days missed because of sickness, and 49% of days they worked while ill.

For the immunized group, however, the authors reported that vaccination reduced the risk of ILI by about 45% and also reduced by at least 60% the number of:

Illness days

Workdays lost

Days worked while sick

Days in bed because of ILI

When exploring for bias, the investigators found that vaccination was not associated with a decrease in non-respiratory illnesses during flu season or a reduced risk of ILI outside of flu season. "Thus, we did not find evidence for selection bias in our data," they wrote.

The true cost of influenzaPrevious studies on the benefits of the flu vaccine for working adults were based mainly on those younger than 50, the authors reported, pointing out that their findings demonstrate that the 50-to-64 age-group can reap the same benefits from immunization as other adult populations.

They pointed out that costs associated with lower work productivity are an important economic burden linked to influenza. They calculated that for each worker, vaccination prevented a mean of .37 work days lost and a mean of 1.45 days of working while ill.

"Studies that fail to account for presenteeism [working while sick] in their estimates of economic burden of influenza may substantially underestimate the impact of illness and the productivity benefits associated with vaccination," the group wrote.

Though the authors did not find a selection bias in their study, they cautioned that the vaccination rate among the participants was higher than the national rate for the 50- to 64-year-old age-group and that the university employees may have been healthier than other Minnesota residents in the same age-group.

"It is not clear how our findings might translate to other types of workers or workers in other settings," they added.

The study covered a single flu season that featured a good match between the circulating influenza strains and the vaccine, the group said, adding the caveat that vaccine efficacy will vary from year to year.

However, Nichol said in the press release that the findings show that flu vaccines have a large impact on health and work productivity in this adult subgroup. "It is a win-win for the worker with fewer illnesses, days of illness, days in bed, etc, and for the employer with improved worker productivity," she said.

Implications for public health policyIn an editorial comment on the study that appeared in the same issue of CID, Gregory A. Poland, MD, a vaccine expert at the Mayo Clinic in Rochester, Minn., wrote that the vaccination payoff the group found "was a huge benefit when the public health impact is considered."

Poland said though the study did not examine culture-proven influenza illnesses, it did explore "in the field" outcomes.

An often-overlooked aspect of presenteeism is safety, he wrote, and working while sick may impair the functioning and judgment in, for example, pilots, physicians, nurses, and law-enforcement officers.

The authors' use of an Internet-based survey is an inexpensive and rapid method that could help public health officials monitor vaccine efficacy in the field, Poland said. "Such technology could prove to be invaluable as a real-time information source to public health officials and private practitioners during the chaos of an influenza pandemic," he added.

Poland called on public health officials to renew efforts to vaccinate working adults against influenza.

"A simplified and impactive public health recommendation should be that all Americans > 6 months of age receive influenza vaccine," he wrote, adding that the Advisory Committee on Immunization Practices has hinted at making the recommendation within the next 2 to 4 years.

The study also underscores the need for a comprehensive adult vaccination program, Poland wrote, "and adequate funding should be provided for such a program."

Data that show the safety and efficacy of flu vaccines need to be shared with policymakers, who often don't know the true morbidity, mortality, and economic burdens associated with influenza, he wrote.